1. Field of the Invention
The present invention relates to medical catheters and more particularly to a multi-lumen balloon for a radiation centering catheter.
2. Description of Related Art
Medical catheters generally include elongate tube-like members that may be inserted into the body, either percutaneously or via a body orifice, for any of a wide variety of diagnostic and interventional purposes. Such catheters are particularly useful with regard to certain cardiovascular applications where the object is to deliver a treatment or instrument to a remote lesion.
Percutaneous Transluminal Coronary Angioplasty (PTCA or balloon angioplasty) is the predominant treatment for coronary vessel stenosis. In PTCA, catheters are inserted into the cardiovascular system via the femoral artery under local anesthesia. A pre-shaped guiding catheter is positioned in the coronary artery, and a dilatation catheter having a distensible balloon portion is advanced through the guiding catheter into the branches of the coronary artery until the balloon portion traverses or crosses a stenotic lesion. The balloon portion is then inflated with a medium to compress the atherosclerosis in a direction generally perpendicular to the wall of the artery, thus dilating the lumen of the artery. Patients treated by PTCA procedures, however, suffer from a high incidence of restenosis, i.e., the same area of the coronary vessel collapses or becomes obstructed.
Recent preclinical and early clinical studies indicate that intervascular radiation after balloon angioplasty can reduce the rate of restenosis caused by intimal hyperplasia. Generally, in an intervascular radiotherapy procedure, a flexible catheter is inserted into the cardiovascular system of a patient and then advanced to the region of the vessel that has been subjected to the angioplasty procedure. A radiation source or a treatment catheter having a radiation source inside it is then advanced through the flexible catheter so that the radiation source reaches the stenosed vascular site and can deliver an effective dose of radiation. After the radiation treatment, the catheter and radiation source are removed.
Because for a given radiation source activity, the intensity of the radiation delivered to a vessel wall varies in inverse proportion to the square of the distance between the radiation source and the vessel wall, it is desirable to hold the radiation source at, or reasonably near, the center of the vessel for a given treatment period. If the source is not centered within vessel, the vessel wall nearest the source may receive an excess of radiation, while the portion of the vessel wall farthest from the source may be underexposed to the radiation.
There are a number of ways to center a radiation source within a vessel. One such way is using a spiral balloon having a central lumen in which the radiation source is advanced to the stenosed vessel site. In a spiral balloon catheter, the balloon is wrapped or molded in a spiral fashion around a flexible centering lumen. When inflated, the balloon outer diameter pushes against the vessel walls while the inner balloon diameter pushes the radiation source lumen toward the center of the vessel.
Spiral balloons have several significant drawbacks when used in intervascular radiotherapy to control restenosis. The first drawback is that because the balloon is wrapped or molded in a spiral shape around the centering lumen of the catheter, the centering effect of the radiation source decreases as the pitch of the turns of the spiral balloon increases. Thus, the fewer turns a spiral balloon has in its configuration, the less centered the radiation source is inside the vessel. Also, if the spiral balloon is over-pressurized, it will lose its spiral shape, thus leading to inconsistent centering of the radiation source. Another drawback with a spiral balloon is that because every spiral is a taper, when the balloon is in a deflated configuration, it creates a stiff catheter with a bulky balloon. This leads to poor access and limits the use of spiral catheters to certain portions of the vascular system. Furthermore, at the end of the intervascular radiation procedure, the tapers create poor refold of the spiral thus making the removal of the balloon catheter difficult for the physician. Another significant disadvantage of using a spiral balloon in intervascular radiation is the spiral balloon's inconsistent blood perfusion ability. Good blood perfusion of the vessel is achieved only when the blood is flowing freely through the spiral cavity created by the balloon. If any portion of the spiral cavity is blocked, then the flow of the blood is also stopped at that point. Thus, blood perfusion may not be adequate.
Another way to center a radiation source within a vessel is to use a segmented balloon catheter having a series of peaks and valleys created by segmenting an ordinary balloon catheter. The segmented balloon centers the centering lumen using the same principle as the spiral balloon catheter.
An additional way to center a radiation source within a vessel is by using a catheter having an outer balloon and an inner balloon disposed within the outer balloon. Generally, the inner and outer balloons are positioned parallel to each other and axially with the catheter shaft. The inner and outer balloons may have a spiral or a segmented configuration. The inner centering balloon may also be a multiple axial lumen balloon, where the lumens extend parallel to the catheter shaft.
Another way to center a radiation source within a vessel is by having a balloon attached to the distal portion of a radioguide catheter. When inflated, the balloon engages the walls of the vessel to center the treatment channel. The balloon may also be configured to include spiral lumens or/and perfusion lumens to permit perfusion of the blood when the balloon is inflated.
Segmented balloon catheters and multiple balloon catheters have many of the same drawbacks as those associated with spiral balloon catheters, including inadequate centering of the radiation source, poor balloon refold, catheter stiffness, bulky balloon configuration, inconsistent perfusion, etc. While balloons configured with spiral lumens or perfusion lumens have a better perfusion capability than single-spiral, segmented, or multiple balloon configurations, they still have some disadvantages, including poor balloon foldability, catheter stiffness, and less than optimal perfusion capability.
Currently, most radioguide centering catheters used in the industry are of the type known in the industry as “tip RX” (RX being “rapid exchange”). Tip RX radioguide centering catheters are characterized by a short guidewire riding length of approximately 5 mm and a guidewire exit notch distal to the centering balloon. Tip RX catheter assemblies have several disadvantages when used in vascular radiation therapy. First, the trackability of the catheter is not consistent in a challenging vascular anatomy, and can go from excellent to poor for no apparent reason. Poor catheter trackability may make it impossible to place the catheter at the desired treatment site, preventing delivery of the radiation therapy. Pushability is similarly problematic with the tip RX catheter. When withdrawing a tip RX catheter, it is also possible to prolapse the guidewire, complicating the procedure. Another disadvantage is that because the guidewire lumen is distal to the balloon, it adds approximately 10 mm to the overall length of the tip. Cardiologists however, prefer to have the tip of the catheter as short as possible in order to prevent potential injury to the artery distal to the treatment site. Another disadvantage of using a tip RX balloon catheter for vascular radiation therapy is that since the exit notch is distal to the balloon, the guidewire must be left in place, thus creating a small but measurable shadow in the radiation dosimetry.
In addition to tip RX balloon catheters, other catheter designs used for vascular radiotherapy employ an “over-the-wire” (“OTW”) guidewire lumen configuration. Currently, these OTW radiation delivery catheters do not provide the capability of centering the radiation source. Furthermore, while an over-the-wire configuration catheter assembly allows for the guidewire to be pulled back during radiation delivery, the guidewire lumen shifts the source away from the center of the catheter, thus making the centering of the radiation source even more problematic.
The manufacture of inflated balloons with diameters in a range of approximately 1.0 to 6.0 millimeters (mm) presents another significant issue with current balloon catheter designs. One of the challenges relates to the stiffness of the balloon. For example, some manufacturers have used several separate small diameter balloons and attached them using glue or other bonding material around a central catheter shaft to form a balloon catheter. Because the glue or bonding material is positioned along the catheter shaft, the catheter is stiff and difficult to use in coronary vessels having tortuous paths. Therefore, this design configuration gives sub-par performance. Others have used an extrusion process to manufacture a multiple balloon radiation centering catheter. During the extrusion process, however, excess material is generated which tends to make the catheter stiff. In addition, because the material used for the radiation source lumen has generally been different than the material used for the guidewire lumen or the centering balloons, the extrusion process is extremely difficult to complete successfully.